1. Field of the Invention
The present invention generally relates to a method of fabricating mixed mode analog devices, and more particularly relates to a method of forming poly insulator poly (PIP) capacitors by using a self-aligned salicide process.
2. Description of the Prior Art
Mixed mode analog devices simultaneously have circuits with digital devices such as amplifiers and analog digital converters and analog devices such as inverters and adders. Also, mixed mode analog devices include MOS devices.
As the semiconductor devices in deep sub-micron process are highly integrated, a capacitor, such as shown in FIG. 1 is introduced in the fabrication of the semiconductor devices.
Referring to FIG. 1 which is a drawing illustrating a conventional capacitor, a shallow trench isolation (STI) structure 12, a transistor gate structure 14, a lightly doped source/drain area 16, a gate spacer 18, and a heavily doped source/drain 20 in sequence are formed on a semiconductor substrate 10. The transistor gate structure 14 is formed while the first polysilicon (poly) layer 22 of the lower electrode of the capacitor is formed. A dielectric layer 24 is formed on the surface of the semiconductor substrate 10. The second poly layer 26 is deposited on the surface of the dielectric layer 24 of the upper first layer 22 used as an upper electrode of the capacitor. The dielectric layer between the first poly layer 22 and the second poly layer 26 is used as the dielectric layer of the capacitor, and also used as the isolation between the first poly layer 22 and the second poly layer 26.
However, this capacitor structure can only be applied in the aforementioned process, but can not be applied in the self-aligned salicide process. Any step of the self-aligned salicide process can not be omitted. Otherwise, capacitors are unable to be formed. Accordingly, a method of forming PIP capacitors by using the self-aligned salicide process is provided.